Device for determining a common-mode signal in a power line communication network

ABSTRACT

A device for determining a common-mode signal in a power line communication network. The device includes a first line, a second line, and a third line that are connected to a first terminal, to a second terminal, and to a third terminal, respectively. The first, the second, and the third terminal are configured to be connected to a phase line, a neutral line, and a protective ground line of the power line communication network, respectively. The device further includes a common-mode choke configured to couple out the common signal from the first, second, and third line, and the common-mode choke is connected to a termination impedance which is higher than an impedance of the power line communication network.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a divisional application of U.S. Ser. No.13/750,454, filed Jan. 25, 2013, which is a continuation of U.S. Ser.No. 13/058,281, filed May 5, 2011, which is a national stage of PCTApplication No. PCT/EP2009/003302, filed May 8, 2009, and claims thebenefit of priority under 35 U.S.C. §119 from European PatentApplication 08014781.2, filed Aug. 20, 2008. The entire content of eachof the foregoing applications is hereby incorporated by referenceherein.

An embodiment of the invention relates to a device for determining acommon-mode signal in a power line communication network.

BACKGROUND

Power line communication (PLC), also called mains communication, powerline transmission or power line telecommunication (PLT), broadband powerline (BPL), power band or power line networking (PLN) is a termdescribing several different systems for using power distribution wiresfor simultaneous distribution of data. A carrier can communicate voiceand data by superimposing an analog signal of the standard 50 or 60 Hzalternating current (AC). For indoor applications, PLC equipment can usehousehold electrical power wiring as a transmission medium. This is atechnique used e.g. for home networking or in home automation for remotecontrol of lighting and appliances without installation of additionalwiring.

In standard PLC systems the signals are transmitted and received in adifferential-mode (DM). Differential-mode signaling is a method oftransmitting information over pairs of wires. At DM signaling one wirecarries signal and the other wire carries the inverse of the signal, sothat the sum of the voltages to ground on the two wires is alwaysassumed to be zero. PLC modems therefore inject a DM signal between aneutral line and a phase line of an outlet of the power line network ofthe household for communication purposes. Another PLC modem can receivesuch DM signals at another outlet and use the DM signal for controllingan appliance associated with the receiving PLC modem.

At in-house power line grids, there are asymmetric elements between thephase line and the neutral line, like e.g. an open light switch, acurrent bar and a fuse cabinet, branches etc. At these asymmetricelements, the DM signals injected by PLC modems are converted tocommon-mode (CM) signals. Multiple input multiple output (MIMO) PLCmodems can use different channels, in particular also common-modesignals, in order to enhance the coverage of PLC systems.

Therefore, there is need for an improved device for a determining acommon-mode signal in a power line communication network.

SUMMARY

It is an object of the invention to provide a device for determining acommon-mode signal in a power line communication network with animproved ability to detect common-mode signals.

This object is solved via device according to claim 1.

Further details of the invention will become apparent from aconsideration of the drawings and ensuing description.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of embodiments and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments andtogether with the description serve to explain principles ofembodiments. Other embodiments and many of the intended advantages ofthe embodiments will be readily appreciated, as they become betterunderstood by reference to the following detailed description. Theelements of the drawings are not necessarily to scale relative to eachother. Like reference numerals designate corresponding similar parts.

FIG. 1 shows a schematic circuit diagram of an embodiment of theinvention,

FIG. 2 shows a schematic circuit diagram of a further embodiment of theinvention,

FIG. 3 shows a schematic circuit diagram of a further embodiment of theinvention,

FIG. 4 shows a schematic circuit diagram of a further embodiment of theinvention,

FIG. 5 shows a schematic diagram for explaining the reception ofmultiple-input multiple-output signals with an embodiment of theinvention.

DETAILED DESCRIPTION

In the following, embodiments of the invention are described. It isimportant to note that all described embodiments in the following may becombined in any way, i.e. there is no limitation that certain describedembodiments may not be combined with others. Further, it should be notedthat same reference signs throughout the figures denote same or similarelements.

It is to be understood that other embodiments may be utilized andstructural or logical changes may be made without departing from thescope of the invention. The following detailed description, therefore,is not to be taken in a limiting sense, and the scope of the presentinvention is defined by the appended claims.

It is to be understood that the features of the various embodimentsdescribed herein may be combined with each other, unless specificallynoted otherwise.

In FIG. 1 a schematic circuit diagram of a device 100 for determining acommon-mode signal in a power line communication network is depicted.The device 100 might be, for instance, a probe in order to determinecommon-mode ingress in a DM power line system. The device 100 might beas well a part of a power line modem that receives power line signals.

The device 100 comprises a first line 102, a second line 104 and a thirdline 106 which are connected to a first terminal 110, to a secondterminal 112 and to a third terminal 114, respectively. A phase line Pmight be connected to the first terminal 110, a neutral line N might beconnected to a second terminal 112 and a protective earth line PE mightbe connected to the third terminal 114.

The device 100 includes a common-mode choke 120 configured to couple outthe common-mode signal from the first line 102, the second line 104 andthe third line 106.

The common-mode choke 120 is connected to a termination impedance 122which is higher than an impedance of the power line communicationnetwork. The power line communication network comprises all lines andappliances and devices connected to the phase line P, to the neutralline N and to the protective earth line PE.

When using a termination impedance 122 with high impedance, e.g. higherthan an impedance of the power line communication network, DM signalstransmitted over the phase line P, the neutral line N and the protectiveearth line PE and, correspondingly, over the first line 102, the secondline 104 and the third line 106 are less influenced than by using atermination impedance which is considerably lower, e.g. adapted to animpedance of the power line communication network, e.g. 50 to 150 Ohm.

In FIG. 2 a schematic circuit diagram of a further device 200 fordetermining a common-mode signal is depicted. The first line 102, thesecond line 104 and the third line 106 are connected to the firstterminal 110, the second terminal 112 and the third terminal 114 bycoupling capacitors C, respectively. The coupling capacitor C serves toisolate the device 200 against direct current signal on the phase lineP, the neutral line N and the protective earth line PE.

The common-mode choke 120 is wrapped around the first line 102, thesecond line 104 and a third line 106 and connected to a terminationimpedance 122 which is higher than the impedance of the power linecommunication network.

The first line 102 is connected via a first transformer 202 to ground,the second line 104 is connected via a second transformer 204 to groundand the third line 106 is connected via a third transformer 206 toground. A first output 212 is connected to the first transformer 202(impedance), a second output 214 is connected to the second transformer204 (impedance) and a third output 216 is connected to the thirdtransformer 206 (impedance).

The first output 212, the second output 214 and the third output 216 areterminated with termination impedances 222, 224, 226, which might havean impedance matching to the impedance of the power line network (e.g.of 50 Ohm), each. The first output 212, the second output 214, and thethird output 216 are used to provide the differential-mode signals whichare present on the first line 102, the second line 104 and the thirdline 106.

A fourth output 218 is connected to the common-mode choke 120. Thefourth output 218 is configured to provide the common-mode signalpresent on the first line 102, the second line 104 and the third line106.

The termination impedance 122 might be realized as an input impedance ofan analog-to-digital converter connected to the common-mode choke 120.The input impedance of an analog-to-digital converter might be governedby the gate of a CMOS transistor. The value for such input impedancesshall be maximal and can normally be between 1 kΩ and 3 kΩ.

The configuration in FIG. 2 is also known as a star topology. However,it is also possible to use a triangle topology.

In FIG. 3 a further schematic circuit diagram of a further device 300for determining a common-mode signal is depicted. In the device 300 thedetermination of the differential-mode signals is performed by a firstamplifier 302, a second amplifier 304 and a third amplifier 306.

One of the inputs of the first amplifier 302 the second amplifier 304and the third amplifier 306 is connected to ground. The other input ofthe first amplifier 302 is connected to the first line 102 between thecommon-mode choke 120 and a first impedance 312. The second input of thesecond amplifier 304 is connected to the second line 104 between thecommon-mode choke 120 and a second impedance 314. The second input ofthe third amplifier 306 is connected to the third line 106 between thecommon-mode choke 120 and a third impedance 316. The outputs of thefirst amplifier 302, the second amplifier 304 and the third amplifier306 are connected to the first output 222 to the second output 224 andto the third output 226, respectively.

With these amplifiers it is possible to determine the differential-modesignals on the first line 102, the second line 104 and the third line106 at the first output 222, the second output 224 and the third output226. The first amplifier 302, the second amplifier 304 and the thirdamplifier 306 are arranged in a star topology. However, also inarrangement in a triangle topology is possible.

In FIG. 4 a measurement setup is depicted to determine the influence ofthe value of the termination impedance 122 to the isolation ordivergence of the differential-mode signals on the first line 102, thesecond line 104 and the third line 106. A generator 400 with a currentor voltage source EC and an internal impedance of 50 Ohms furthercomprises a fourth impedance 402 of 75 Ohm common to the phase line P,the neutral line N and the protective earth line PE and a fifthimpedance 404, a sixth impedance 406 and a seventh impedance 407 of 50Ohm each, wherein the fifth impedance 404 situated is in the phase lineP, the sixth impedance 406 is situated in the neutral line N and theseventh impedance 407 is situated in the protective earth line PE. Thus,the generator 400 has an assumed differential-mode impedance of 100 Ohmand a common-mode impedance of 150 Ohm (if the terminal of theprotective earth line PE is left open).

A verification with the network analyzer showed that in case thetermination impedance 122 is 50 Ohm only, only a small isolation betweenthe signals on the first line 102 and the third line 106 is present.However, the isolation between the differential-mode signals on thedifferent lines 102, 104, 106 is higher, and thus the coupling lower, ifthe termination impedance is higher, e.g. 1 kΩ or infinite.

In FIG. 5 a schematic diagram showing the feeding possibilities andreceiving possibilities in a multiple input multiple output (MIMO)scheme are depicted. A first power line communication modem 500transmits signals to a second power line communication modem 502 over apower line communication network 504. There are three possibilities forfeeding signals into the power line communication network 504.

A differential-mode signal might be fed between the phase line P and theneutral line N, a differential-mode signal might be fed between thephase line P and the protective earth line PE and a differential-modesignal might be fed between the neutral line N and the protective earthline PE. Due to Kirchhoff s laws only two independent paths arepossible. It is advisable to use the two best possibilities with respectto e.g. noise properties in order to feed the signals into the powerline communication network 504.

On the receiving side there are four possibilities to receive thesignals. It is possible to determine the differential-mode signalbetween phase line and neutral line, to determine the differential-modesignal between phase line P and protective earth PE and to determine thedifferential-mode signal between the neutral line N and the protectiveearth line PE. In addition it is possible to detect the common-modesignal CM by using e.g. the common-mode choke 120.

With a proposed device for determining a common-mode signal and a powerline communication network there is no longer a lost isolation betweenthe three differential-modes (balanced or symmetrically) between thelines.

Multiple-input multiple-output (MIMO) communication signals are fed orreceived symmetrically or balanced between the phase line P and theneutral line N, the phase line P and the protective earth line PE and/orthe neutral line N and the protective earth line PE. Multiple-inputmultiple-output technologies show maximum gain compared to signal inputsignal output schemes if individual signals provide maximum divergence.

With the proposed device a coupling between individual differential-modesignals is reduced, thus increasing the performance of MIMO technology.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and equivalent implementations may besubstituted for the specific embodiments shown described withoutdeparting from the scope of the described embodiments. This applicationis intended to cover any adaptations of variations of the specificembodiments discussed herein. Therefore, it is intended that thisinvention be limited only by the claims and the equivalence thereof.

What is claimed is:
 1. A Power Line Communication (PLC) device,comprising: a phase line coupled to a phase line terminal; a neutralline coupled to a neutral line terminal; a protective earth line coupledto a protective earth terminal; and a first high pass filter connectedin line with the protective earth line.
 2. The device according to claim1, wherein the first high pass filter includes a capacitor and iscoupled to a first inductive element.
 3. The device according to claim2, wherein the protective earth line is coupled to the first inductiveelement and a second inductive element.
 4. The device according to claim1, further comprising: a second high-pass filter connected in line withthe phase line, a first end of the second high-pass filter being coupledto the phase line terminal, and a second end of the second high-passfilter being coupled to a first impedance element; and a third capacitorconnected in line with the neutral line, a first end of the thirdcapacitor being coupled to the neutral terminal, and a second end of thethird capacitor being coupled to a second impedance element, wherein thefirst and second high pass filters include first and second capacitors,respectively.
 5. The device according to claim 1, further comprising afirst capacitor connected in line with the phase line, a first end ofthe first capacitor being coupled to a first impedance element.
 6. Thedevice according to claim 5, further comprising a second capacitorconnected in line with the neutral line, a first end of the secondcapacitor being coupled to a second impedance element.
 7. The deviceaccording to claim 6, wherein a second end of the first capacitor iscoupled to the phase line terminal, wherein a second end of the secondcapacitor is coupled to the neutral line terminal, and wherein a firstend of the first high pass filter is coupled to a first inductiveelement.
 8. The device according to claim 7, wherein the first inductiveelement is a transformer.
 9. The device according to claim 6, whereinthe first capacitor and second capacitors are isolation capacitors toisolate the device against direct current signals in the phase andneutral lines, respectively.
 10. The device according to claim 6,wherein the first high pass filter is coupled to a third impedanceelement.
 11. The device according to claim 1, wherein the first highpass filter is coupled to an impedance element having a value of 50Ohms.
 12. The device according to claim 11, wherein the impedanceelement is different from a first inductive element coupled to the firsthigh pass filter.
 13. The device according to claim 1, wherein a firstend of the first high pass filter is coupled to the protective earthterminal, and wherein a second end of the first high pass filter iscoupled to a first inductive element.
 14. The device according to claim1, wherein said device is a multiple-input and multiple-output (MIMO)Power Line Communication (PLC) modem to receive symmetrical or balancedinput communication signals and has a plurality of inputs and aplurality of outputs, and wherein said modem is one of a plurality ofsaid modems included in a local power line network.
 15. The deviceaccording to claim 14, wherein a number of inputs to said modem differsfrom a number of outputs from said modem.